The present invention relates to a device of controlling the idling speed of an internal combustion engine.
An idling speed control device has been known in which a bypass passage is branched off from the intake passage of an engine, which is located upstream of a throttle valve, and connected again to the intake passage located downstream of the throttle valve, and a diaphragm type vacuum operated control valve device is arranged in the bypass passage. The diaphragm vacuum chamber of the control valve device is connected via a vacuum conduit to the intake passage located downstream of the throttle valve, and an electromagnetic control valve is arranged in the vacuum conduit for controlling the cross-sectional area of the vacuum conduit. In this idling speed control device, at the time of idling, the level of the vacuum produced in the diaphragm vacuum chamber of the control valve device is controlled by controlling the electromagnetic control valve in accordance with the operating condition of the engine and, in addition, the air flow area of the bypass passage is controlled in accordance with a change in the level of the vacuum produced in the diaphragm vacuum chamber. As a result of this, the amount of air fed into the cylinders of the engine from the bypass passage is controlled. However, in such a conventional idling speed control device, firstly, in the case wherein a vehicle is used in a cold region, the electromagnetic control valve becomes frozen and, thus, it is impossible to control the cross-sectional area of the vacuum conduit. As a result of this, since it is also impossible to control air flow area of the bypass passage, a problem occurs in that it is impossible to control the amount of air fed into the cylinders from the bypass passage. Secondly, in a conventional idling speed control device, since the diaphragm type vacuum operated control valve device is used, the controllable range of the air flow area of the bypass passage is very narrow. Therefore, even if the control valve device is fully opened, air, the amount of which is necessary to operate the engine at the time of fast idling, cannot be fed into the cylinders of the engine from the bypass passage. Consequently, in a conventional idling speed control device, an additional bypass passage is provided in addition to the regular bypass passage, and a valve, which is actuated by a bimetallic element, is arranged in the additional bypass passage. When the temperature of the engine is low, the valve, which is actuated by the bimetallic element, opens. As a result of this, since additional air is fed into the cylinders of the engine from the additional bypass passage in addition to the air fed into the cylinders of the engine from the regular bypass passage, the amount of air, which is necessary to operate the engine at the time of fast idling, can be ensured. As mentioned above, in a conventional idling speed control device, since the additional bypass passage and the valve, actuated by the bimetallic element, are necessary in addition to the regular bypass passage, a problem occurs in that the construction of the idling speed control device will be complicated. In addition, since the amount of air fed into the cylinders of the engine is controlled by only the expanding and shrinking action of the bimetallic element at the time of fast idling, there is a problem in that it is impossible to precisely control the amount of air fed into the cylinders of the engine.
An object of the present invention is to provide a novel device of controlling the idling speed, which device is capable of precisely controlling the amount of air flowing within the bypass passage at the time of idling and maintaining the idling speed of the engine at an optimum speed.
According to the present invention, there is provided a device of controlling the idling speed of an engine of a vehicle having an air conditioning apparatus for cooling a driver's compartment, said engine comprising a main intake passage, a throttle valve arranged in the main intake passage, a bypass passage branched off from the main intake passage upstream of the throttle valve and connected to the main intake passage downstream of the throttle valve, a control valve arranged in the bypass passage, and a step motor actuating the control valve for controlling the amount of air flowing within the bypass passage, said air conditioning apparatus comprising an air duct which interconnects the driver's compartment to an exterior of the vehicle, a suction fan arranged in the air duct, an evaporator arranged in the air duct, a heat exchanger arranged in the air duct at a position located downstream of the evaporator, and an air mixture damper arranged in the air duct between the evaporator and the heat exchanger for controlling the amount of air directly flowing into the driver's compartment and for controlling the amount of air flowing into the driver's compartment via the heat exchanger, wherein said device comprises: first means for detecting the engine speed to produce a first signal indicating the engine speed; second means for detecting the operating condition of the engine to produce a second signal indicating that the engine is operating in an idling state; third means arranged in the air duct for producing a third signal indicating the temperature of air which has passed through the evaporator; fourth means cooperating with the air mixture damper for producing a fourth signal indicating that the entire air directly flows into the driver's compartment without passing through the heat exchanger, and; electronic control means in response to said first signal, said second signal, said third signal and said fourth signal for rotating the step motor in a rotating direction wherein the engine speed approaches a predetermined desired idling speed when the engine is operating in an idling state, said desired idling speed being increased when the temperature of air which has passed through the evaporator is higher than a predetermined temperature and when said fourth means produces said fourth signal.
The present invention may be more fully understood from the description of preferred embodiments of the invention set forth below, together with the accompanying drawings.